Electrical transformer

ABSTRACT

An electrical transformer wherein a plurality of electrical coils are wound on separate coil forms. The plurality of coils are each attached to a separate insulating washer member, with the coil leads also being fixed to the washer member. The coils and washer members are disposed on a common insulating tube in side-by-side relation, and a magnetic core is assembled about the coils, including a portion which extends through the opening in the common insulating tube. The coil forms and common insulating tube provide the coil to core insulation, while the insulating washer members provide barrier insulation between the coils.

United States Patent [l5] 3,657,677 Hunt et al. [4 Apr. 18, 1972 [54] ELECTRICAL TRANSFORMER 2,159,269 5/1939 Hasse ..336/206 x ,3 l [72] Inventors: Clarence W. Hunt, Transfer; Ralph W. 3 2 $332 et a] n Johnston; Wald Stephens, both of 2,980,874 4/1961 Tarbox 336/206 Sharpsville, all of Pa. 7 Z Primary Examiner-Thomas J. Kozma 3] Assignee gzsrtrlnglgouse Electric Corporation, Pitt Ammey A; T- Stratton and Donald R Lackey [22] Filed: Feb. 10, 1971 [57] ABSTRACT [21 1 Appl. No.: 114,207 An electrical transformer wherein a plurality of electrical coils are wound on separate coil forms. The plurality of coils are Related US. Application Data each attached to a separate insulating washer member, with the coil leads also being fixed to the washer member. The coils [62] g'g g 835918 June 1969 and washer members are disposed on a common insulating tube in side-by-side relation, and a magnetic core is assembled about the coils, including a portion which extends through the [52] US. Cl ..336/96, 336/192 Opening in the common insulating tube The coil forms and l- 15/02,}[01f27/30 common insulating tube provide the coil to core insulation, Fleld of Search 193 while the insulating washer members provide barrier insulation between the coils. [56] References Cited 7 Claims, 2 Drawing Figures UNITED STATES PATENTS 1,960,033 5/1934 Smith ..336/l98 X ELECTRICAL TRANSFORMER CROSS REFERENCE TO RELATED APPLICATION BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates in general to electrical apparatus, and more specifically to new and improved electrical transformers of the dry type.

2. Description of the Prior Art Dry type transformers such as control transformers for switchgear, lighting transformers, boosting transformers and the like, are commonly constructed with concentric high and low voltage coils, which are assembled with a magnetic core. The resulting magnetic core-coil assembly is often encapsulated or potted in cast solid insulation to protect the transformer from moisture, dirt, and explosive or corrosive fumes. This construction has certain disadvantages. For example, the heat generated in the inner coils of the concentric arrangement must traverse the insulation disposed between the coils, as well as traversing the outer coils, before reaching the solid insulation. Special precautions must also be taken to insure that the electrical leads will extend outwardly from the cast solid insulation in the proper spaced relation, or special mounting brackets for the leads must be incorporated with the assembly. The transformers must be constructed to specific ratings and ratios, as it is not practical to form'subassemblies which may be stocked and subsequently assembled to provide different ratings and ratios. Thus, it would be desirable to be able to improve heat transfer from the windings in potted or encapsulated type electrical transformers, enabling a savings in magnetic core and conductive material to be realized, as well as to provide a construction which lends itself to new and improved methods of manufacturing transformers of this type, which methods reduce the manufacturing cost of the apparatus.

SUMMARY OF THE INVENTION structed to facilitate the manufacturing of the transformer.

More specifically, the transformer coils are each wound separately on an insulated tubular coil form, and the coils are fastened to an insulating washer member. The coil leads are also fixed to this washer member, to properly position them for subsequent encapsulation, if used. Then, the desired number and type of electrical coils are disposed on a common insulating tube, which holds the coils in assembled relation, and facilitates the stacking of a magnetic core through and about the coils. Encapsulation of the magnetic core-coil as sembly provides mechanical restraint for maintaining the assembled relation of the magnetic core and coils. The coils, being axially spaced, instead of concentrically or radially spaced, each contact the solid insulation for more efficient cooling. The insulating coil forms and the common insulating tubular member, which initially provide mechanical support for each coil, and the assembled group of coils, now function as the coil to ground insulation. The insulating washer members, which initially support the coils and their electrical leads, now provide barrier insulation between the axially spaced coils.

2 BRIEF DESCRIPTION OF THE DRAWINGS Further advantages and uses of the invention will become more apparent when considered in view of the following detailed description and drawings, in which:

FIG. 1 is a partially exploded perspective view of an electrical coil assembly constructed according to the teachings of the invention, and

FIG. 2 is an elevational view, partially in section, of the coil assembly shown in FIG. 1 assembled with a magnetic core and encapsulated in solid insulation.

DESCRIPTION OF PREFERRED EMBODIMENT Referring now to the drawings, and FIG. 1 in particular, there is shown a new and improved coil assembly 10 constructed according to the teachings of the invention, which is for transformers of the dry type, and preferably for those potted in cast solid insulation. In this instance, coil assembly 10 has four electrical coils l2, l4, l6 and 18, which are spaced axially apart on a common center line, but any number of coils may be used, depending upon the specific application. Electrical coil 12 and its associated insulating members are shown exploded, inorder to more clearly illustrate a new and improved method of assembling a coil in subassemblies, and the coils l4, l6 and 18 are illustrated in assembled relation.

The new and improved coil assembly 10 may be best understood by describing a new and improved method of constructing the coil assembly. First, each of the coils, such as coil 12, is wound individually on an insulating tubular coil form member 20 having an opening 22 therein, with the coil form member being formed of any suitable insulating material such as a plurality of layers of Kraft-paper, or a form constructed of non-cellulostic material, such as synthetic resin, as desired. The opening 22 is substantially rectangular in configuration, in order to receive a rectangular winding leg of the magnetic core assembly, as will be hereinafter described.

means, such as by tape which is washer member 36. The insulating washer Individual coil sections of approximately square cross-sectional configuration, facilitate their winding on high speed automatic winding equipment. The coil 12 is wound on the coil form 20, with the coil 12 being wound of insulated electrical conductor, such as enamel coated copper wire, providing electrical leads 24 and 26 at the end of the coil, which project upwardly from the upper surface of the coil. After the winding step has been completed, each of the coils are attached to a fiat thin insulating washer member, such as washer member 28, which has an opening 30 therein having the same configuration and dimensions as opening 22 in coil form 20. Coil 12 is attached to insulating washer member 28 by any suitable tightly wound about the coil and washer member, with the tape being threaded through the openings 22 and 30 at predetermined spaced locations. For example, tape loops 32 and 34 are illustrated mechanically securing coil 14 in assembled relation with an insulating member may have a depression in its outer periphery, such as depression 38 in washer member 28, for orienting the application of the tape. In like manner, the coils 16 and 18 are secured to insulating washer members 40 and 42, respectively.

The next step is to properly position and secure the coil leads for the subsequent manufacturing steps. This is accomplished by attaching first and second discrete auxiliary electrical leads to each of the insulating washer members, such as by stapling, and then attaching the coil leads to the ends of the first and second auxiliary leads. For example, first and second auxiliary leads 44 and 46 are attached to insulating washer member 28 by staples 48 and 50, respectively. Auxiliary leads 44 and 46 may each be an electrically conductive wire covered with insulation, except at its extreme ends. The ends of the auxiliary leads adjacent the leads from the coil, are fixed to the coil leads, while the remaining ends of the auxiliary leads extend outwardly from assembly 10, and are adapted for connection to external circuits. The insulating washer members may have a projection thereon, upon which the auxiliary leads are stapled, such as the projection 31 on washer member 28.

More specifically, coil lead 24 of electrical coil 12 is fixed electrically and mechanically to end 52 of auxiliary lead 44, while coil lead 26 is fixed electrically and mechanically to end 54 of auxiliary lead 46. In like manner, electrical coil 14 is associated with auxiliary leads 54 and 56, which are connected to coil leads 56 and 60 respectively, coil 16 is associated with auxiliary leads 62 and 64, and coil 18 is associated with auxiliary leads 66 and 68. The ends of the coil leads may be crimped directly to the ends of the auxiliary leads by mechanical crimping apparatus designed to break through the enamel coating on the coil wire, making it unnecessary to strip the insulation from the coil wire, or to solder the leads together.

Thus, up to this point, individual coil sections may be manufactured and ledgered as to wire size, number of turns, and the like, enabling any combination of coils to be removed from stock for a specifically required coil assembly. When a coil assembly is to be manufactured, the coils having the required wire size and number of turns are stacked in side-by-side relation on a common tubular insulating member 70, which has an opening 72 therein. The outer configuration of insulating member 70 is selected and sized to snugly fit the openings 30 and 22 in the insulating washer member 28 and coil form 20, respectively. Insulating member 70 has an overall length sufficient to accommodate the desired number of electrical coils and their associated insulating washer members, as well as an auxiliary insulating washer member 72 which is disposed on the extreme end of the tubular insulating member 70, adjacent the electrical coil that is not already sandwiched between the two insulating washer members, such as at the end of electrical coil 12.

The tubular insulating member 70 positions, aligns, and supports the plurality of axially spaced coils and their insulating washer members, and provides a dimensionally accurate opening 72 through which laminations of a magnetic core may be disposed or stacked while assembling the magnetic core about the coils. The laminations may be conventional E-I laminations formed of magnetic steel, with the positions of the E and I laminations being reversed from layer to layer to increase the mechanical strength of the core assembly; or, magnetic core assemblies of the wound type may be used.

Coil assembly 10 shown in FIG. 1 thus comprises a plurality of electrical coils l2, 14, 16 and 18, a plurality of coil form members, such as coil form member 20, with each coil being wound on its own individual coil form member, and a tubular insulating member sized to snugly fit the openings in the coil forms, with the length of the insulating member being selected to accommodate the number of electrical coils. The coils are telescoped over the tubular insulating member in axially spaced, side-by-side relation, and an insulating washer member is disposed between each of the coils, and at the end of the outer coils, with the coil leads being secured to the insulating washer members. The coil forms and tubular insulating members initially support the individual coils, and hold the plurality of coils in assembled relation, respectively, and in the final coil assembly function to provide the necessary insulation between the coils and the magnetic core. The insulating washer members provide barrier insulation between the coils, and at the ends of the outer coils, without impeding the flow of heat away from the coils, and also may be used to orient and support the electrical leads, as well as providing support for 'the individual coils. Further, each coil is equally exposed to the atmosphere, or to the encapsulating solid insulation, enabling heat generated in the coils to be uniformly and efficiently dissipated. It will be noted that none of the coils are buried concentrically within the other coils, which thus eliminates the normal high-low insulation between the coils and the barrier to heat transfer which it presents.

While the coil assembly 10 may be used with any type of construction, it is especially suitable for use in encapsulated or potted transformers. FIG. 2 is an elevational view of a transformer 80, partially in section, which includes the coil assembly 10 in FIG. 1, assembled with a magnetic core 82 to provide a magnetic core-coil assembly 84, which is encapsulated in solid insulation 86. Like reference numerals in FIGS. 1 and 2 indicate like components.

More specifically, magnetic core 82 includes a plurality of metallic laminations 88 which are stacked to provide the desired magnetic circuits through and about the electrical coils. As hereinbefore stated, the magnetic core 82 may be also of the wound type, if desired, such as the type which includes two pairs of C-cores, each assembled through the opening in the tubular member 22 and banded to hold each pair to C-cores in assembled relation. The magnetic core-coil assembly is disposed in a metallic tank or casing 90, and suitably positioned therein, such as with brackets which guide and hold the magnetic core, or the extensions of the washer members may be used to space the magnetic core-coil assembly from the casing walls, eliminating the need for special brackets. The solid insulation 86 completely encapsulates the magnetic core-coil assembly 84, extending outwardly from the assembly 84 to the walls of the casing. The solid insulation 88 may be of any suitable type, such as a therrnosetting resin, or a thermoplastic resin having a softening temperature well above the maximum operating temperature of the coils. The resin system utilized may be filled with suitable filler means, to enhance its heat transfer characteristics. The filler may be finely divided silica, such as sand, or any other suitable organic, non-friable material. Suitable resin systems for encapsulating transformers of this type are disclosed in US. Pat. No. 3,030,597, which is assigned to the same assignee as the present application. A typical procedure for encapsulating electrical apparatus of this type is to heat the casing 90 and the magnetic core-coil assembly 84 to a predetermined temperature, such as 135 C, preparatory to receiving a liquid casting resin, such as an epoxy resin. Liquid resin is poured into the casing to a predetermined level. A finely divided filler material, such as sand, is then introduced into the casing until the resin level rises above the uppermost part of the magnetic core-coil assembly. The casing 90 may be vibrated while the resin and sand are introduced, to insure complete impregnation of the assembly with the liquid resin, and to uniformly disperse the filler material throughout the resin. After the resin and filler have been introduced, the whole assembly is heated to gel and cure the insulation to a solid.

A A KVA single-phase, 60 Hz transformer having two primary and two secondary coils, and a voltage ratio of 240 X 480 to /240 was constructed according to the teachings of the invention. Heat transfer from the coils was found to be substantially improved over the prior art concentric coil arrangement, enabling the transformer to be made smaller for the same rating, while still operating within the temperature rise of the larger prior art transformer construction. The size reduction made possible by the improved heat transfer characteristics of the new and improved transformer resulted in a savings of 15 percent in the cost of coil wire and magnetic core material.

The coil assembly 10 also enables cost savings to be realized in the manufacture of the transformer. The coils are individually wound on separate coil forms and attached to washer members. The coil leads are secured to a washer member in the desired position. Then, coils having the desired electrical characteristics may be selected from stock to provide the required coil assembly, with the coils being aligned over a tight fitting tubular insulating member, which holds the coils in assembled relation and provides coil to ground insulation. The coil forms upon which the individual coils are wound also add to the coil to ground insulation, and the insulting washer members provide barrier insulation between the various coils. Thus, the insulating members which initially facilitate the manufacturing of the coil assembly, also provide the function of electrically insulating the coils from one another and from ground, as well as orienting and fixing the electrical leads from the coils in the desired spaced relation.

We claim as our invention:

1. An electrical transformer comprising:

I a plurality of electrical coils, each of said electrical coils having an opening therein and electrical leads,

a plurality of insulating coil fonn members, each having an opening therein,

each of said coil form members being disposed in an opening in one of said electrical coils,

a tubular insulating member,

said plurality of electrical coils being disposed in axially spaced, side-by-side relation on said tubular insulating member, with the opening in each coil form member being sized to snugly fit the outer configuration of said tubular insulating member,

insulating washer members having an opening therein, said washer members disposed on said tubular insulating member, adjacent the electrical coils disposed at each end of the axially spaced electrical coils.

3. The electrical transformer of claim 1 including solid insulating means, said solid insulating means encapsulating the magnetic core-coil assembly.

4. The electrical transformer of claim 1 wherein the means securing the electrical leads of the coils to the insulating washer members are separate electrical leads stapled to the insulating washer members, with the separate electrical leads being electrically connected to the ends of the coil leads.

5. The electrical transformer of claim 1 including a casing, with the magnetic core-coil assembly disposed in said casing, and solid electrical insulating means disposed in said casing, said solid electrical insulating means encapsulating said magnetic core-coil assembly.

6. The electrical transformer of claim 5 wherein said solid electrical insulating means includes a thermoset resin and a finely divided inorganic filler.

7. The electrical transformer of claim 1 including insulating tape wound about each coil and an adjacent insulating washer member, through the openings in the coil and insulating washer member. 

1. An electrical transformer comprising: a plurality of electrical coils, each of said electrical coils having an opening therein and electrical leads, a plurality of insulating coil form members, each having an opening therein, each of said coil form members being disposed in an opening in one of said electrical coils, a tubular insulating member, said plurality of electrical coils being disposed in axially spaced, side-by-side relation on said tubular insulating member, with the opening in each coil form member being sized to snugly fit the outer configuration of said tubular insulating member, insulating washer members having an opening therein, said insulating washer members being disposed on said tubular insulating member, with at least one disposed in each of the spaces between said axially spaced coils, means securing the electrical leads of each of said plurality of electrical coils to an immediately adjacent insulating washer member, and a magnetic core disposed in inductive relation with said plurality of electrical coils, including a portion which extends through the opening in said tubular insulating member, to provide a magnetic core-coil assembly.
 2. The electrical transformer of claim 1 including insulating washer members disposed on said tubular insulating member, adjacent the electrical coils disposed at each end of the axially spaced electrical coils.
 3. The electrical transformer of claim 1 including solid insulating means, said solid insulating means encapsulating the magnetic core-coil assembly.
 4. The electrical transformer of claim 1 wherein the means securing the electrical leads of the coils to the insulating washer members are separate electrical leads stapled to the insulating washer members, with the separate electrical leads being electrically connected to the ends of the coil leads.
 5. The electrical transformer of claim 1 including a casing, with the magnetic core-coil assembly disposed in said casing, and solid electrical insulating means disposed in said casing, said solid electrical insulating means encapsulating said magnetic core-coil assembly.
 6. The electricAl transformer of claim 5 wherein said solid electrical insulating means includes a thermoset resin and a finely divided inorganic filler.
 7. The electrical transformer of claim 1 including insulating tape wound about each coil and an adjacent insulating washer member, through the openings in the coil and insulating washer member. 